medwireNews: Non-Hispanic Black women with hormone receptor-positive, HER2-negative, early breast cancer have worse outcomes than their non-Hispanic White counterparts despite similar genetic risk and treatment adherence in the first year, suggests an analysis of the RxPONDER trial.

The differences in outcomes “were observed despite analyzing a carefully chosen and uniformly treated study population, suggesting that biological factors other than disparities in care may be contributing to inferior outcomes in racial minorities,” said investigator Yara Abdou (The University of North Carolina at Chapel Hill, USA) in a press release.

Speaking at the 2022 San Antonio Breast Cancer Symposium in Texas, USA, Abdou explained that the RxPONDER study established the clinical utility of the 21-gene recurrence score (RS) in women with hormone receptor-positive, HER2-negative early breast cancer with 1–3 positive lymph nodes and an RS of 25 or lower, and showed that the benefit of add-on adjuvant chemotherapy differed by menopausal status.

The current analysis focused on “clinicopathologic characteristics, survival outcomes and race in association with the recurrence score” in the 4048 RxPONDER participants who had reported their race and ethnicity, she added.

The investigator said that there was no significant difference in the RS distribution between the 70.0% of participants who were non-Hispanic White, the 6.1% who were non-Hispanic Black, the 15.1% who were Hispanic, the 8.0% who were Asian, and the 0.8% who were Native American/Pacific Islander. The proportion of patients with an RS of 0–13 ranged from 39.0% to 43.0%, while the proportion with an RS of 14–25 ranged from 57.0% to 61.0%.

There was also no difference across the racial cohorts with regard to the number of involved lymph nodes and tumor size, but there were differences in histologic grade, such that non-Hispanic Black participants had fewer low-grade (22 vs 27%) and more high-grade (18 vs 10%) tumors than non-Hispanic White participants.

Non-Hispanic Black patients also had higher BMI scores than those of other races, with for instance 35% of non-Hispanic Black patients having a BMI of at least 35 kg/m² compared with 18%, 16%, 2%, and 27% of non-Hispanic White, Hispanic, Asian, and Native American/Pacific Islander patients, respectively.

Survival analysis showed that the 5-year invasive disease-free survival (IDFS) rate was lower for the non-Hispanic Black cohort, at 87.2%, than for the non-Hispanic White, Hispanic, and Asian cohorts, at 91.5%, 91.4%, and 93.9%, respectively. The Native American/Pacific Islander cohort was not included in the survival analyses due to low number of events.

The unadjusted hazard ratio (HR) for invasive disease for non-Hispanic Black versus non-Hispanic White patients was a significant 1.39, which remained comparable, at 1.37, after adjustment for RS, treatment arm, menopausal status, age, and grade, albeit with borderline statistical significance. However, after BMI was added to the multivariable model, the association lost significance and the HR attenuated to 1.21.

“In terms of treatment effect, there was no significant interaction between race and treatment arm in either postmenopausal or premenopausal groups,” said the presenter. But she highlighted that “definitive conclusions about racial differences in treatment benefit cannot be made due to the limited number of events in the [non-Hispanic] Black cohort.”

The findings were similar for distant relapse-free survival (DRFS), with 5-year rates of 90.1% and 94.7% for non-Hispanic Black and White participants, respectively, and an unadjusted significant HR for distant relapse of 1.39, which reduced to a nonsignificant 1.31 in the multivariable model including BMI.

The researchers also assessed treatment compliance, finding that non-Hispanic Black patients were significantly more likely than their non-Hispanic White counterparts to accept the treatment assignment (93 vs 86%) and as likely to adhere to endocrine therapy at 6 months (98.0 vs 96.6%) and 12 months (96.0 vs 94.8%).

“These data suggest that the outcome differences are less likely attributable to lack of treatment compliance within the first year,” said Abdou, adding that they “plan to assess the likelihood of treatment completion and adherence by race and ethnicity beyond the first year.”

The team will also explore social determinants of health based on geographic location as “[o]utcome differences may remain due to health care access issues,” which can persist even in a clinical trial setting.